1. A verb in command form with a direct object. "It" can define almost anything.
2. A term used to promote the use of an activity, often coupled with peer pressure.
3. Colloquial for sexual intercourse. Often used before one has the maturity to pronounce the word 'sex'.

1. Do it! Clean the dishes!
2. "I'm not smoking this joint..."
"DO IT! Smoke the joint! Once isn't gonna hurt!"
3. Ah, c'mon, me and Jessica do it all the time without condoms.

One of the shortest yet most powerful phrases in the English language, the use of "DO IT!" has been inadvertently sending young men to jail and/or the hospital since sometime in the early 1920's. If anything bad happens in your life, it's probably because one of your friends yelled this at you.

Prosecuting Attorney: And at what point did you decide that it would be a good idea to "T-bag" Officer Jones?